1. Field of the Invention
This invention relates to certain aminomethyl phenylimidazole derivatives which selectively bind to brain dopamine receptor subtypes. This invention also relates to pharmaceutical compositions comprising such compounds. It further relates to the use of such compounds in treating affective disorders such as schizophrenia and depression as well as certain movement disorders such as Parkinsonism. Furthermore compounds of this invention may be useful in treating the extraparamidyl side effects asssociated with the use of conventional neuroleptic agents. The interaction of aminomethyl phenylimidazole derivatives of the invention with dopamine receptor subtypes is described. This interaction results in the pharmacological activities of these compounds.
2. Description of the Related Art
Schizophrenia or psychosis is a term used to describe a group of illnesses of unknown origin which affect approximately 2.5 million people in the United States. These disorders of the brain are characterised by a variety of symptoms which are classified as positive symptoms (disordered thought, hallucinations and delusions) and negative symptoms (social withdrawal and unresponsiveness). These disorders have an age of onset in adolescence or early adulthood and persist for many years. The disorders tend to become more severe during the patients lifetime and can result in prolonged institutionalization. In the US today, approximately 40% of all hospitalized psychiatric patents suffer from schizophrenia.
During the 1950's physicians demonstrated that they could sucessfully treat psychotic patients with medications called neuroleptics; this classification of antipsychotic medicatin was based largely on the activating (neuroleptic) properties of the nervous system by these drugs. Subsequently, neuroleptic agents were shown to increase the concentrations of dopamine metabolites in the brain suggesting altered neuronal firing of the dopamine system. Additional evidence indicated that dopamine could increase the activity of adenylate cyclase in the corpus striatum, an effect reversed by neuroleptic agents. Thus, cumulative evidence from these and later experiments strongly suggested that the neurotransmitter dopamine was involved in schizophrenia.
One of the major actions of antipsychotic medication is the blockade of dopamine receptors in brain. Several dopamine systems appear to exist in the brain and at least three classes of dopamine receptors appear to mediate the actions of this transmitter. These dopamine receptors differ in their pharmacological specificity and were originally classified upon these differences in the pharmacology of different chemical series. Butyrophenones, containing many potent antipsychotic drugs were quite weak at the dopamine receptor that activated adenylate cyclase (now known as a D1 dopamine receptor). In contrast, they labelled other dopamine receptors (called D2 receptors) in the subnanomolar range and a third type D3 in the nanomolar range. Phenothiazines possess nanomolar affinity for all three types of dopamine receptors. Other drugs have been developed with great specificity for the D1 subtype receptor.
Recently, a new group of drugs (such as sulpiride and clozapine) have been developed with a lesser incidence of extrapyramidal side effects than classical neuroleptics. In addition, there is some indication that they may be more beneficial in treating negative symptoms in some patients. Since all D2 blockers do not possess a similar profile, hypotheses underlying the differences have been investigated. The major differences have been in the anticholinergic actions of the neuroleptics as well as the possilility that the dopamine receptors may differ in motor areas from those in the limbic areas thought to mediate the antipsychotic responses. The existence of the D3 and other as yet undiscovered dopamine receptors may contribute to this profile. Some of the atypical compounds possess similar activity at both D2 and D3 receptors. The examples of this patent fall into this general class of molecules.
Using molecular biological techniques it has been possible to clone cDNAs coding for each of the pharmacologically defined receptors. There are at least two forms of D1. and two forms of D2 dopamine receptors. In addition, there is at least one form of D3 dopamine receptor. Examples from the aminomethyl phenylimidazole series of this patent possess differential affinities for each receptor subtype.